Extramedullary Hematopoiesis in the Mandibular Lymph Node of Simian-Human Immunodeficiency Virus-Infected Rhesus Monkeys (Macaca mulatta): A Report of Three Cases

Three cases of extramedullary hematopoiesis (EMH) in the mandibular lymph nodes of rhesus monkeys, experimentally infected intravenously with a chimeric simian human immunodeficiency virus, are described. On histopathologic evaluation, multiple sections of mandibular lymph node from all animals showed evidence of EMH, which included erythroid, myeloid, or megakaryocytic precursor cells (or all) within the medullary sinuses. Immunohistochemistry was used for positive identification of multiple cell types. Evidence of EMH was not observed in numerous sections of axillary, inguinal, cervical, hilar, or mesenteric lymph nodes or in any other tissues examined. To our knowledge, this is the first report on EMH within the lymph nodes of rhesus monkeys without an obvious underlying disease process or stringent blood-sampling schedule warranting the need for increased hematopoiesis outside the confines of the bone marrow.

Increased inherent intestinal granzyme B expression may be associated with SIV pathogenesis in Asian non-human primates

BACKGROUND

Unlike Asian non-human primates, chronically SIV-infected African non-human primates (NHP) display a non-pathogenic disease course. The different outcomes may be related to the development of an SIV-mediated breach of the intestinal mucosa in the Asian species that is absent in the African animals.

METHODS

To examine possible mechanisms that could lead to the gut breach, we determined whether the colonic lamina propria (LP) of SIV-naïve Asian monkeys contained more granzyme B (GrB) producing CD4 T cells than did that of the African species. GrB is a serine protease that may disrupt mucosal integrity by damaging tight junction proteins.

RESULTS

We found that the colonic LP of Asian NHP contain more CD4(+) /GrB(+) cells than African NHP. We also observed reduced CD4 expression on LP T cells in African green monkeys.

CONCLUSION

Both phenotypic differences could protect against SIV-mediated damage to the intestinal mucosa and could lead to future therapies in HIV(+) humans.

Dendritic cells enhance detection of antigen-specific cellular immune responses by lymphocytes from rhesus macaques immunized with an HIV envelope peptide cocktail vaccine

Detection and enumeration of functional antigen-specific T cells is important for understanding the breadth of cell-mediated immunity to infections and experimental vaccines. We tested the utility of dendritic cells (DC), the professional antigen presenting cells, in the enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) for efficient monitoring of antigen-specific immunity in rhesus macaques vaccinated with an HIV envelope peptide-cocktail. Compared with direct antigen-specific stimulation of peripheral blood mononuclear cells, the DC-ELISPOT protocol involving co-culturing of macaque T cells with autologous DC pulsed with the various peptides from the vaccine cocktail yielded up to 18-fold higher numbers of interferon-gamma producing cells without increasing the background. Importantly, use of DC in the analyses revealed immune responses in vaccinated macaques that were otherwise undetectable. Similar data were obtained when recall responses to purified protein derivative were analyzed by the DC-ELISPOT method using blood samples from human volunteers. These data establish the importance of DC in improving detection sensitivity and eliminating false negative results, both essential for efficient monitoring of antigen-specific cellular immune responses.

Protection against chronic infection and AIDS by an HIV envelope peptide-cocktail vaccine in a pathogenic SHIV-rhesus model

Based on our prior studies in mouse, monkey, chimpanzee, and human experimental systems, we identified six peptides encoded by highly conserved regions of the human immunodeficiency virus type 1 (HIV-1) envelope gene that selectively induce cellular immune responses in the absence of anti-viral antibody production. We tested a cocktail of the six peptides as a prototype vaccine for protection from simian human immunodeficiency virus (SHIV) infection and acquired immunodeficiency syndrome (AIDS) in a rhesus monkey model. Three monkeys were vaccinated with the peptide cocktail in Freund's adjuvant followed by autologous dendritic cells (DC) pulsed with these peptides. All the vaccinated animals exhibited significant induction of T-cell proliferation and cytotoxic T lymphocytes (CTL) responses, but no neutralizing antibodies. Two control mock-vaccinated monkeys showed no specific immune responses. Upon challenge with the pathogenic SHIV(KU-2), both the control and vaccinated monkeys were infected, but efficient clearance of virus-infected cells was observed in all the three vaccinated animals within 14 weeks. These animals also experienced a boosting of antiviral cellular immune responses after infection, and maintained antigen-specific IFN-gamma-producing cells in circulation beyond 42 weeks post-challenge. In contrast, the two mock-vaccinated monkeys had low to undetectable cellular immune responses and maintained significant levels of viral-infected cells and infectious virus in circulation. Further, in both the control monkeys plasma viremia was detectable beyond 38 weeks post-challenge indicating chronic phase infection. In one control monkey, the CD4+ cells dropped to very low levels by 2 weeks post-challenge and became undetectable by week 39 coinciding with high plasma viremia and AIDS, which included cachexia and ataxia. These results serve as proof of principle for the effectiveness of the HIV envelope peptide cocktail vaccine against chronic infection and AIDS, and support the development of multivalent peptide-based vaccine as a viable strategy to induce cell-mediated immunity (CMI) for protection against HIV and AIDS in humans.

Differences in functional immune responses of high vs. low hardy healthy individuals

An association between the personality trait of hardiness and immune responses was explored. Blood samples were collected from 21 healthy individuals under nonstressful conditions, who had either high or low levels of hardiness. Functional immune assays tested for natural killer (NK) cell activity and proliferation responses to Candida albicans (Candida), purified protein derivative from Mycobacterium tuberculosis (PPD), lipopolysaccharide (LPS), concanavalin A (Con A), and Staphylococcus enterotoxin A (Staph A). Differences between high and low hardy groups on these immune responses were examined using Bonferroni adjusted independent t-tests. Results revealed significant differences between the groups for Candida, PPD, Con A, and Staph A. In all instances, the high hardy group had larger mean proliferative responses than the low hardy group. Implications of the study as well as avenues for future research are discussed.

Impairment of antigen-specific cellular immune responses under simulated microgravity conditions

Microgravity has been implicated to play a role in the observed immune dysfunction of astronauts and cosmonauts after either short-term or long-term space travel. These reports, together with studies describing increased levels of microorganisms in the space cabin environment suggest potential risk for in-flight incidences of infectious diseases. In order to understand the mechanism underlying these immune defects, it is important to have a ground-based model that would reliably mimic the effects of microgravity on antigen-specific immune function. We tested the utility of the rotating wall vessel (RWV) technology developed at NASA as a model system because in the RWV the culture medium and the cells rotate synchronously with the vessel, thereby creating simulated microgravity conditions. We compared the RWV to the conventional tissue culture flask (T-flask), for culturing immune precursor cells with cytotoxic T lymphocyte (CTL) activity against synthetic viral peptides. We observed a significant loss of antigen-specific CTL activity in RWV cultures, but not in those from the T-flask, irrespective of the peptide immunogen used for inducing the primary immune response in different mouse strains. Loss of CTL activity in RWV cultures coincided with a significant reduction in CD8+ cells as well as CD4+ cells and DEC205+ dendritic cells, suggesting adverse effects of RWV culturing on both the effector and accessory cells for the loss of antigen-specific CTL function. These results provide a strong parallel to the reported defects in cell-mediated immunity during space travel and strongly support the utility of the RWV technology as an effective ground-based model for identifying key steps in immune cell dysfunction related to microgravity.

Presence of HLA-C-restricted cytotoxic T-lymphocyte responses in long-term nonprogressors infected with human immunodeficiency virus

Approximately 5% of people with human immunodeficiency virus type 1 (HIV-1) infection remain free of disease for 10 or more years. These long-term nonprogressors (LTNPs) exhibit lower viral loads and stable CD4+ lymphocyte counts. The immunologic basis for this disease-free condition is not known. Because cytotoxic T lymphocytes (CTLs) constitute a major immune defense mechanism for sustained recovery from viral infections, we analyzed HIV-specific CTL responses in three asymptomatic LTNPs. We observed the presence of HIV-1 envelope-specific CTL responses mediated by HLA class I C-restricted CD8+ cells in these individuals. Using autologous target cells and a panel of HLA-matching and -mismatching B-cell lines as targets, we determined that HLA-Cw7 is the restricting element for the observed CTL activity. Additionally, we identified three peptides, one previously not reported, from conserved regions in the envelope protein as CTL epitopes. We previously reported these peptides to be efficient in inducing HIV-specific cellular immune responses in murine and nonhuman primate models. Our results support the role of the HLA-C locus in generating CTL responses and constitute the first report of an HLA-Cw7-restricted HIV-1 envelope-specific CTL response in HIV+ LTNPs, which may be important in the control of HIV replication in vivo.

A synthetic peptide from the first conserved region in the envelope protein gp160 is a strong T-cell epitope in HIV-infected chimpanzees and humans

We reported earlier that synthetic peptides corresponding to highly conserved regions in the envelope protein gp160 of the human immunodeficiency virus type 1 (HIV-1), in particular an 11-amino acid sequence (peptide 104) from the first conserved region at the amino-terminus, were capable of inducing strong HIV-specific T-cell proliferative responses in several inbred mouse strains as well as in outbred Rhesus monkeys. We have now obtained evidence of the presence of significant levels of proliferative response to peptide 104 in 7 of 9 chimpanzees chronically infected with HIV-1 (p < or = 0.05) and 8 of 17 HIV+ individuals (p < or = 0.001). Further, four other conserved HIV envelope-derived peptides, identified previously in our murine and Rhesus monkey model systems, were widely recognized as T-cell epitopes in both chimpanzees and humans infected with HIV-1. In none of the infected subjects did peripheral blood mononuclear cells show proliferative responses to unrelated control peptides. Also, neither the control normal chimpanzees nor HIV-seronegative individuals showed proliferative responses to the conserved peptides. With respect to the humoral responses, serum samples from none of the chimpanzees showed reactivity with any of the conserved peptides, and only low levels of antibody responses against peptide 104 were observed in 3 of the 17 patients (p > 0.05). Importantly, three of the conserved envelope-derived peptides, including peptide 104, overlap with sequences that were reported in the literature to be epitopes for virus-induced cytotoxic T lymphocytes in asymptomatic HIV+ individuals. These observations, together with our results in multiple animal models and humans, establish that these conserved HIV envelope-derived peptides, particularly peptide 104, are significant T-cell epitopes with potential usefulness for induction of HIV-specific cell-mediated immune responses in humans.

Expression of human immunodeficiency virus type I tat results in down-regulation of bcl-2 and induction of apoptosis in hematopoietic cells

Infection by human immunodeficiency virus type 1 (HIV-1) is characterized by progressive loss of various cell types, mainly CD4+ T lymphocytes. While a passive role for the virus in cell destruction is recognized, it does not account for the vast amount of cell death including those of uninfected "bystander' cells. Since in the past we and others have demonstrated the capacity of the Tat protein of HIV-1 to modulate the expression of various cellular genes and that Tat secreted by HIV-infected cells can be readily taken up by various cell types, we have investigated the role of Tat on inducing apoptosis. Our results indicate that T lymphocytes transfected to constitutively express HIV-1 tat, when grown under serum-free conditions results in rapid apoptosis characterized by typical ultrastructural features and DNA fragmentation. Additionally, we observed that in several hematopoietic cell types, including T and B lymphoid cells and monocytoid cells, the expression of HIV-1 tat results in down-regulation of bcl-2, an oncogene with known potential for inhibition of apoptosis. The tat-mediated down-regulation of bcl-2 was observed at both the transcriptional and translational levels. Also, tat-transfected cells expressed increased amounts of bax, a bcl-2 family protein known to induce apoptosis. While these results support reports in the literature of an active role for tat in inducing cell death in HIV-infected individuals, they point to a new mechanism involving Tat-mediated modulation of bcl-2 and bax.

Cross-reactive T-cell proliferative responses to V3 peptides corresponding to different geographical HIV-1 isolates in HIV-seropositive individuals

We have investigated the proliferative response of peripheral blood mononuclear cells from individuals infected with human immunodeficiency virus type 1 (HIV-1) to synthetic peptides from the third variable loop region (V3) in the envelope protein gp120. We tested a total of 14 peptides, corresponding to 14 HIV-1 isolates belonging to four geographical locations (clades U, A, B, and D). Although differences in relative level of responses exist between individual peptides and patients, the proliferation in response to all 14 V3 peptides was significantly greater than that to unrelated control peptides. Additionally, we observed that proliferative responses of blood cells from the 10 HIV-seropositive individuals studied from the clade B region to peptides from within clades U, A, B, and D were not significantly different, indicating the cross-reactive nature of the V3-specific cell-mediated immune responses. Even though the majority of patients also exhibited antibody responses against several V3 peptides, serum samples from 50% of clade B patients exhibited antibody cross-reactivity, while proliferative responses to V3 peptides from more than one clade were observed in 80% of patients. Importantly, in two patients, decreased CD4+ cell numbers, an important surrogate marker of disease progression, significantly correlated with loss of V3 peptide-specific proliferative responses but not antibody responses. These results have important implications toward evaluating the utility of V3 peptides for designing therapeutic and/or vaccine reagents against HIV-1.

Cross-reactive cytotoxic T lymphocytes induced by V3 loop synthetic peptides from different strains of human immunodeficiency virus type 1

Recent efforts at understanding the immune response generated against human immunodeficiency virus (HIV) infection have focused on cytotoxic T lymphocyte (CTL)-mediated recognition of HIV antigens. CTLs are a major immune defense mechanism and are necessary for the recovery of many viral infections. We have previously developed a method for screening synthetic peptides for the ability to induce virus-specific major histocompatibility complex-restricted CTLs in mice. Using this method, we now report the identification of peptides from the V3 region in gp120 of seven different HIV-1 strains that are capable of inducing a virus-specific CD8+ CTL response in vivo. V3 peptides from MN and SC strains of HIV-1, which are representative of typical strains found in North America and Europe, induced CTLs that exhibited cross-reactivity against a broad range of HIV-1 strains. In addition, immunization of mice with a mixture of these V3 peptides resulted in efficient CTL responses directed against the corresponding HIV-1 strains. These data, together with information in the literature describing the CTL epitope nature of V3 peptide from HIV-1 IIIB in the context of several HLA alleles, indicate the possibility of including V3 synthetic peptides as components of potential vaccines for inducing broadly cross-reactive CTL response against a diverse array of HIV-1 strains.

Studies on V3-specific cross-reactive T-cell responses in chimpanzees chronically infected with HIV-1IIIB

OBJECTIVE AND DESIGN

In this study we used synthetic peptides corresponding to the third variable region (V3) in the envelope protein gp120 of 14 different HIV-1 strains, and tested whether V3-specific T-cell responses are HIV-1 strain-specific or broadly cross-reactive in nine chimpanzees chronically infected with HIV-1IIIB.

METHODS

Peripheral blood mononuclear cells isolated from nine HIV-infected chimpanzees and two uninfected controls were tested, by the [3H]-thymidine incorporation assay, for proliferative responses against phytohemagglutinin, control peptide and V3-loop peptides corresponding to 14 different HIV-1 strains. Serum samples collected from the chimpanzees were analyzed by enzyme-linked immunosorbent assay for antibodies against the V3 peptides.

RESULTS

Chimpanzees 100, 139 and 175 exhibited high level of proliferative response directed against the cognate V3 peptide from HIV-1IIIB and also showed cross-reactivity to V3 peptides from 13, seven and 13 of 13 other HIV-1 strains, respectively. Additionally, five out of nine chimpanzees showed cross-reactive proliferative responses to V3 peptides from at least eight different HIV-1 strains, while significant proliferation to V3 peptides from two or more HIV-1 strains was observed in seven out of nine chimpanzees. On the other hand, four out of nine chimpanzees showed antibody response directed against the cognate V3 peptide from HIV-1IIIB, and serum from only one chimpanzee (100) showed cross-reactive antibody to six different V3 peptides.

CONCLUSIONS

Overall, these studies in chimpanzees chronically infected with HIV-1IIIB indicate that with respect to the immunodominant V3 region, the virus-induced T-cell immunity is directed against a broad spectrum of HIV-1 strains.

Studies on in vivo induction of HIV-1 envelope-specific cytotoxic T lymphocytes by synthetic peptides from the V3 loop region of HIV-1 IIIB gp 120

We have previously reported the induction of MHC class I-restricted, CD8+ cytotoxic T lymphocytes (CTLs) specific to human immunodeficiency virus type 1 (HIV-1) in mice by a 15-amino acid peptide (R15K) from the V3 loop in gp120. We now present evidence showing that CTL activity induced by R15K was stable for 8-10 weeks after a single injection and that as little as 20 micrograms peptide was sufficient for efficient CTL induction in vivo. While induction of CTLs was efficient with R15K emulsified in either complete or incomplete Freund's adjuvant, only a low-level CTL response was observed in mice immunized with R15K in either alum or saline. We analyzed a series of carrier-free synthetic peptides ranging in length from 8 to 24 amino acids from the V3 loop region and observed that peptide R10I consisting of 10 amino acids from the middle portion of R15K was more efficient for CTL induction. Additionally, lymph node cells from mice immunized with 24 and 15 amino acid peptides (N24G and R15K, respectively) when restimulated in vitro with R10I exhibited greater HIV-1 env-specific CTL activity than when either of the longer peptides was used for restimulation. A peptide consisting of only 8 amino acids (R8K) was sufficient neither for inducing primary CTLs nor for in vitro restimulation of lymph node CTL precursors. These results establish that a carrier-free 10-amino acid synthetic peptide from the V3 loop region in HIV-1 gp120 has the optimal sequence for efficient induction of HIV env-specific CTLs in mice.

Studies on in vivo induction of cytotoxic T lymphocyte responses by synthetic peptides from E6 and E7 oncoproteins of human papillomavirus type 16

Induction of cytotoxic T lymphocyte (CTL) responses is an important defense mechanism against infectious agents, specifically viruses. In the present investigation we employed a mouse assay system we previously developed, for rapid induction of CTLs by synthetic peptides from E6 and E7 oncoproteins of human papillomavirus type 16 (HPV-16). In particular, we compared the efficiency of CTL induction by HPV-16 peptides synthesized as linear monomers with those containing a dipalmitoyl-lysine-glycine-glycine (P2-KGG) moiety at the amino-terminus. Our results identified a 15-amino-acid peptide from E6(Q15L, aa 43-57) to be capable of inducing CTLs in vivo and addition of the lipid tail significantly increased CTL induction over that seen with the linear form of the peptide. Further, we identified a shorter peptide, V1OC, with 9 of 10 amino acids overlapping with Q15L peptide (aa 49-58) to be capable of inducing CTLs against both V1OC and Q15L. In case of E7 protein, our results demonstrated usefulness of P2-KGG moiety for enhanced CTL induction by previously identified CTL epitope peptides Q19D (aa 44-62) and R9F (aa 49-57). CTLs induced by both the E6 and E7 peptides were MHC class I-restricted and exhibited strict allele specificity and CD8+ phenotype. Our results showing enhanced cell-mediated immune responses with lipid-tailed forms of peptides add strength to the concept of a synthetic peptide-based vaccine for prophylaxis and therapy of HPV-associated cervical cancer.

Use of helper T cell-inducing peptides from conserved regions in HIV-1 env in a noncovalent mixture with a CTL-inducing V3-loop peptide for in vivo induction of long-lasting systemic CTL response

Our previous reports established that immunization of mice in the footpad with a 15-amino acid synthetic peptide (R15K) from the V3 loop region in the envelope protein gp120 of human immunodeficiency virus type 1 (HIV-1) resulted in rapid induction of major histocompatability complex (MHC) class I-restricted, CD8+ HIV-1 envelope-specific cytotoxic T lymphocytes (CTLs) in the proximal popliteal lymph node. While efficient CTL activity could be assayed in lymph node cells for 8 to 10 weeks after a single injection, spleen cells from these mice showed low to negligible levels of specific CTLs at 4 to 8 weeks postimmunization. We tested immunizing mice with a noncovalent mixture of a helper T cell (Th) activity-inducing peptide and R15K and observed efficient induction of R15K-specific CTL response that could be assayed up to 8 weeks postimmunization in cells obtained from both lymph node and spleen. Efficient CTL priming was observed when Th peptides from either of two different conserved regions in the HIV env were mixed with R15K, containing a dipalmityl-lysine-glycine-glycine moiety at the amino terminus. These data confirm reports in literature describing requirement of Th activity for efficient priming of CTL response in vivo. Additionally, these studies strongly suggest the possibility of formulating potential vaccine candidates consisting of mixtures of synthetic peptides capable of inducing Th and CTL responses in the context of multiple MHC haplotypes.

Inhibition of human immunodeficiency virus type 1 infection and syncytium formation in human cells by V3 loop synthetic peptides from gp120

Because V3 loop-specific antibodies have been shown to inhibit human immunodeficiency virus type 1 (HIV-1) infection of human cells and because specific mutations in the V3 loop render the virus ineffective for infection and syncytium formation, we tested the anti-HIV effects of V3 loop peptides from different HIV-1 strains. We obtained evidence that V3 loop synthetic peptides of 8 to 15 amino acids at nanogram concentrations efficiently blocked HIV-1 IIIB infection of several human T-cell lines and of freshly prepared normal human T cells. More importantly, syncytium formation by three different primary clinical HIV isolates was inhibited by the V3 loop peptide from HIV-1 IIIB at a concentration of 1 micrograms/ml. Concentrations of V3 peptides up to 50 micrograms/ml were not toxic to any of the human cells studied. Additionally, V3 peptides incubated in normal human serum or plasma exhibited biological and physical stability for up to 24 h. Taken together, these results suggest that the V3 loop peptides have medical utility as therapeutic reagents to either prevent HIV-1 infection in humans or reduce the spread of virus infection in HIV-infected individuals. These findings are especially significant because a number of reports in the literature indicate that the V3 loop region in gp120 plays an important role in the initial stages of HIV-1 infection of cells.

Induction of human immunodeficiency virus-specific T cell responses in rhesus monkeys by synthetic peptides from gp160

We have previously identified several synthetic peptides from conserved regions of the human immunodeficiency virus (HIV) envelope protein gp160 that have the capacity to induce broadly reactive T cell responses against gp160 in mice of several major histocompatibility complex (MHC) haplotypes. In the present investigation three rhesus monkeys were immunized with a mixture of eight synthetic peptides that are capable of inducing T cell activity in mice. Peripheral blood mononuclear cells (PBMCs) from these monkeys were monitored every 2 weeks for a period of 34 weeks for proliferative responses against individual peptides and recombinant gp160. Peripheral blood mononuclear cells from all three rhesus monkeys showed good proliferative responses with peptides 104 (aa 45-55), 111 (aa 118-130), and 63 (aa 519-543), whereas weak responses were observed with peptides 113 (aa 204-216) and 116 (aa 240-252). Two of the three rhesus monkey-derived PBMC preparations also showed good proliferative responses with peptide 61 (aa 586-598). Significant responses were not observed with peptides 105 (aa 48-61) and R15K (aa 315-329) in any of the monkeys immunized. However, PBMCs from all three monkeys showed significantly high proliferative responses with recombinant gp160, the HIV-1 envelope protein precursor. These results demonstrate that mixtures of synthetic peptides from HIV env gene product can prime gp160-specific T cell responses in rhesus monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Immobilization of amyloglucosidase

Enzymatic hydrolysis of starch for the production of glucose syrups of various compositions has assumed considerable commercial significance due to the extensive application of these syrups in food and beverage industries. Hydrolysis of starch to glucose involves liquefaction of the gelatinized starch with acid or thermostable alpha-amylase followed by saccharification to glucose by amyloglucosidase. Large scale saccharification of liquefied starch to glucose using soluble enzyme is time consuming and requires 48-72 hr at pH 4.5 and 55-60 degrees C. Since, by replacing soluble amyloglucosidase with immobilized enzyme, it is possible to reduce the conversion time, several methods have been tried to obtain a highly active and stable immobilized preparation capable of converting high concentrations of liquefied starch to glucose. However, till today, immobilized amyloglucosidase has not found industrial application as no immobilized system has shown high temperature stability and conversion efficiency comparable to that of the soluble enzyme.

Rapid in vivo induction of HIV-specific CD8+ cytotoxic T lymphocytes by a 15-amino acid unmodified free peptide from the immunodominant V3-loop of GP120

Efforts to generate a vaccine to prevent infection by human immunodeficiency virus (HIV) have focused on inducing neutralizing antibodies. However, cytotoxic T-lymphocyte (CTL) responses are a major immune defense mechanism required for recovery from many different virus infections. Since CTL epitopes can be defined by short synthetic peptides, we searched for HIV peptides that elicit a viral-specific CTL response in mice. We have developed a new method for screening CTL-inducing peptides involving a single injection into the footpad of mice to prime CTLs in the draining popliteal lymph node of mice within 10 days. Our results demonstrate that a 15-amino acid peptide (aa 315-329) derived from the V3 loop of HIV gp120 caused a rapid induction of peptide-specific and gp160-specific CD8-positive CTLs. Lysis of targets is specific since cells preincubated with unrelated peptides are resistant to lysis as are cells of a different MHC haplotype pretreated with the cognate peptide. Pretreatment of restimulated node cells with complement plus anti-CD8 but not anti-CD4 removed the lytic activity. We also successfully induced in vivo CTL activity with unmodified synthetic peptides from the influenza and Sendai virus nucleoproteins, indicating general applicability of our method for rapid screening of CTL epitopes. Because HIV replication has been reported by several labs to occur mainly in lymph nodes of infected patients, the rapid induction of HIV-specific CTLs in proximal lymph nodes by unmodified peptides emphasizes the physiological significance of our findings toward vaccine and therapeutic approaches.

Membrane-permeable dideoxyuridine 5'-monophosphate analogue inhibits human immunodeficiency virus infection

2',3'-Dideoxyuridine (ddU) is ineffective at controlling human immunodeficiency virus type 1 (HIV-1) infection in human T cells, because it is not biotransformed to the active 5'-triphosphate. The metabolic block resides in the poor substrate affinity of ddU for cellular nucleoside kinases. This problem cannot be overcome by supplying the preformed nucleotides, because such compounds are unable to penetrate cells. To circumvent the requirement of ddU for enzymic phosphorylation, we have prepared bis(pivaloyloxymethyl) 2',3'-dideoxyuridine 5'-monophosphate (piv2 ddUMP), as a potential membrane-permeable prodrug of ddUMP, and investigated its metabolism and anti-HIV activity in two human T cell lines, one with wild-type thymidine kinase activity (MT-4) and the other deficient in thymidine kinase activity (CEM-tk-). The 5'-mono-, di-, and triphosphates of ddU were formed in both cell lines after exposure to piv2-ddUMP. In contrast, phosphorylated metabolites were not observed in cells treated with ddU or ddUMP alone. piv2-ddUMP also reduced the cytopathic effects of HIV-1 in MT-4 cells (ED50, 4.75 microM) and inhibited virus production in culture fluid (ED50, 20 microM). In addition, piv2-ddUMP protected CEM-tk- cells from HIV-1 infection, as demonstrated by inhibition of intracellular p24 antigen levels (ED50, 3 microM) and reverse transcriptase activity in culture medium (Ed50, 2.5 microM). Based on these findings, we propose that the "masked nucleotide" strategy may make available for development nucleoside analogues hitherto considered inactive because of failure to undergo biotransformation to the corresponding 5'-monophosphates. Moreover, by circumventing metabolic dependency on nucleoside kinases, the strategy may overcome acquired resistance to nucleoside analogues caused by the loss or depletion of nucleoside kinases.